(1) Field of the Invention
The present invention relates to an amorphous metal-metal composite article and a method for producing the same, and more particularly relates to an amorphous metal-metal composite article, comprising an ordinary crystallized metal and an amorphous material (hereinafter may be referred to as amorphous), such as amorphous metal or amorphous alloy, which has been produced from its melted state through rapid cooling and has no crystal structure, firmly bonded to the crystallized metal by the explosion pressure of an explosive, and a method for producing the same.
Amorphous metal has excellent magnetic properties, and hence is attempted to be used as various magnetic materials.
(2) Related Art Statement
Amorphous can be produced by a rapid cooling method or other various methods, such as spatter method, chemical vapor deposit method, plating method and the like. However, the amorphous obtained by these methods are thin sheets, fine wires and powders, all of which have a dimension of less than several hundreds .mu.m, and the use field of these amorphouses is very limited. In order to use amorphous in a wide field, amorphous having a larger dimension is demanded, and a shaped article produced by the compression molding of amorphous metal powder has been disclosed (Japanese Patent Laid-open Specification No. 61-139,629).
Japanese Patent Laid-open Specification No. 61-195,905 discloses an amorphous-covered metal obtained by a method wherein an amorphous metal powder is bonded to a metal matrix by an explosion pressure; and Japanese Patent Laid-open Specification No. 62-23,905 discloses a method for producing a composite sintered article from an amorphous metal powder and a metal powder by utilizing a high energy shock.
There has been proposed a technic, wherein an amorphous metal thin sheet having a thickness of not larger than 100 .mu.m is bonded to a sheet or round rod of metal by an explosion pressure to produce a composite article having both of the excellent magnetic properties inherent to amorphous metal and the high strength inherent to metal (Magnetic Society of Japan, 10th Autumn Annual Meeting Preprint No. 4PC-10 (page 61) (1986, 11), Ichiro Sasada et al, "Properties of Torque Sensor produced by the Explosion Bonding Method"). Further, Japanese Patent Laid open Specification No. 61-132,282 discloses a method for bonding an amorphous metal to a metal by an explosion pressure in order to produce an amorphous metal-metal composite article which has a clearance between the amorphous metal and the metal and is used as an electrode in a chlorine-generating electrolysis.
As a method for bonding a metal thin sheet having a thickness of about 100 .mu.m to a metal sheet by an explosion pressure, there has been known a method, for example, illustrated in FIG. 2. In the method of FIG. 2, a metal thin sheet 2' is adhered to a metal sheet 1' having a thickness of about 1-2 mm by the use of an adhesive 3', an explosive layer 4' is arranged on the metal sheet 1' at the surface opposite to the surface adhered with the metal thin sheet 2', the laminate of the metal thin sheet 2', metal sheet 1' and explosive layer 4' is arranged such that the surface of the metal thin sheet 2', which surface is opposite to the surface adhered with the metal sheet 1', is faced with a clearance to a metal 5' to be bonded with the metal thin sheet 2', and the explosive 4' is detonated to apply an explosion pressure through the metal sheet 1' having a thickness of 1-2 mm to the metal thin sheet 2' and to collide the metal thin sheet 2' to the metal 5' at a high velocity.
It is known that, when it is intended to bond a metal sheet to another metal sheet, for example, to bond a sheet of a metal, such as titanium or the like, to a steel sheet, a good result is obtained by previously polishing the surfaces of both the metal sheets to a surface roughness of not larger than approximately 0.7 .mu.m and then bonding both the members to each other (Japanese Patent Application Publication No. 42-24,982).
In the conventional amorphous metal-metal composite article produced by the use of amorphous metal powder, the amorphous metal portion has a block shape, round rod shape or annular shape having a certain thickness. Moreover, the amorphous metal portion is produced by compacting powders. Therefore, the conventional amorphous metal-metal composite article is poor in strength, and can not be used, for example, as a torque sensor for detecting the torque of engine.
In order to eliminate these drawbacks, there has been proposed to produce a sintered article by the use of a combination of an amorphous metal powder and a metal powder. However, the resulting sintered article is still insufficient in the strength. Moreover, a minute observation of the amorphous metal sintered body portion shows that the portion is formed of individual particles of powders bonded to each other, and therefore the amorphous metal sintered body portion has a slight magnetical strain at the boundary of the particles, and the resulting sintered shaped article is apt to be poor in the magnetic properties as a whole.
Conventional method for producing a composite article of an amorphous metal thin sheet and a metal sheet is free from the drawbacks of the conventional sintered article produced by the use of a combination of an amorphous metal powder and a metal powder, which drawbacks are poor in the strength of the resulting shaped article and in the magnetic properties at the bonding boundary of fellow particles, but still has several drawbacks. One of the drawbacks is that the amorphous metal thin sheet has a thickness of 100 .mu.m or less, and predominantly has a thickness of about 20-30 .mu.m, and therefore when it is intended to bond the amorphous metal thin sheet to a metal sheet by an explosion pressure, the amorphous metal thin sheet is deformed, and a composite article having a smooth surface can not be obtained, or only a composite article having locally bonded portions is obtained. Further, during the bonding of the amorphous metal thin sheet to the metal sheet, the bonding interface of the amorphous metal thin sheet and the metal sheet is exposed to a high temperature, and the amorphous metal thin sheet is often crystallized in many portions due to the high temperature, and excellent magnetic properties are lost in the resulting composite article. Moreover, although a method, wherein an amorphous metal thin sheet is collided to a metal at a high velocity to bond them with each other, can be carried out in principle, it is practically difficult to produce a composite article having a good bonded state, and the method can not be practically used.
The inventors have variously studied the drawbacks of the above described conventional methods in order to find out an effective means for bonding an amorphous metal thin sheet to a metal sheet.
There are probably the following two reasons as a reason why an amorphous metal thin sheet bonded to a metal does not have a smooth surface.
(1) In the conventional method for bonding a metal sheet to another metal sheet or a metal block by utilizing an explosion pressure, as illustrated in FIG. 3, a metal sheet 2" is arranged in parallel to a metal sheet 5" with a small clearance, an explosive layer 4" is arranged so as to be in contact with that surface of the metal sheet 2" which is opposite to the surface faced to the metal sheet 5", the explosive 4" is detonated from its one end to fly the metal sheet 2" at a high velocity by the explosion pressure and to collide the metal sheet 2" to the metal sheet 5", whereby the collision point is continuously moved corresponding to the proceeding of the explosion, and the metal sheet 2' is bonded to the metal sheet 5". In this method, when the metal sheet 2" is thin, the metal sheet 2" is plastically deformed or sometimes broken due to the strain caused by the explosion pressure during the course of the flying by the explosion pressure before the collision to the metal sheet 5", and a distorted composite article or a composite article, wherein the metal sheet 2" in a broken state is bonded to the metal sheet 5", is often obtained. Particularly, when it is intended to use an amorphous metal sheet, which is a subject material to be used in the present invention, in place of the metal sheet 2", and to bond the amorphous metal sheet to a metal sheet 5", the amorphous metal sheet is often broken before its collision with the metal sheet 5" or often bonded unsatisfactorily to the metal sheet 5" by an undesirable strain due to the reason that the amorphous metal sheet is hard but is poor in deformability and further is thin.
(2) It has been thought that the above described drawbacks of the deformation and breakage of the metal sheet 2" during its flying can be obviated, for example, by a method, wherein a metal sheet 2' is adhered to a metal sheet 1' having a thickness of about 1-2 mm by means of an adhesive 3' and an explosion pressure is applied to the metal sheet 2' through the metal sheet 1' as described above. However, although the metal sheet 2' is prevented from being deformed and broken during the course of flying, a mutual plastic fluidization of the metal sheet 2' and the metal sheet 5' occurs at the bonding interface of both the members during the course of the bonding thereof, and the plastic fluidization has an adverse influence upon the shape of the surface of the metal sheet 2' to form often a corrugate surface or to form often a composite article having a broken surface. The reason is probably as follows. It has been known that, when metals are bonded to each other by the explosion, it is necessary that the collision point of both the metals moves at a velocity lower than the sound velocity in either the metal sheet 2' or the metal sheet 5'. It has been known that, when this requirement is satisfied, a plastic fluidization occurs at the interface of the metal sheet 2' and the metal sheet 5', and both the metal sheets are firmly bonded with each other while when this requirement is not satisfied, the metal sheet 2' and the metal sheet 5' are repelled with each other, and are not bonded with each other. That is, when it is intended to bond a metal to a metal or to bond an amorphous metal to a metal by the use of explosion pressure in a conventional technic, it is an essential requirement to cause a plastic fluidization at their bonding interface, and if the plastic fluidization does not occur, both the metal sheets are not able to be bonded with each other. However, the essential requirement for attaining the bonding is the cause of the deformation of the surface of an amorphous metal thin sheet or the breakage of the amorphous metal thin sheet during the bonding of the thin sheet to a metal sheet. That is, there is an antinomy in the bonding of an amorphous metal thin sheet to a metal sheet. Particularly, amorphous metal has a high hardness and is difficult to be deformed, and when it is intended to deform forcedly an amorphous metal thin sheet by applying a large strain, the amorphous metal thin sheet is broken. Therefore, the above described problems probably highly influence upon amorphous metal thin sheet higher than upon ordinary metals.
In order to solve the above described problems, the followings are considered.
(1) In order to prevent the deformation of an amorphous metal thin sheet during the course of flying by the explosion pressure, the flying distance should be made small as possible, and if possible, the amorphous metal thin sheet should be bonded to a metal sheet without the flying of the amorphous metal thin sheet by the explosion pressure.
(2) In order to make small as possible the plastic fluidization at the bonding interface of an amorphous metal thin sheet with a metal sheet, the collision point of both the sheets at their bonding interface should be moved at a velocity higher than the higher sound velocity between the sound velocity in the amorphous metal thin sheet and that in the metal sheet to suppress the plastic fluidization as small as possible and a novel method for bonding both the sheets in a satisfactorily high strength should be developed.
(3) Even when the above described requirements have been attained, it is necessary to suppress the crystallization of amorphous metal as low as possible in order to maintain the excellent properties of the amorphous metal. Therefore, the width of the range, in which the amorphous metal reaches its crystallization temperature, should be made small as possible.
The inventors have made various theoretical and experimental investigations for attaining these requirements, and have accomplished the present invention.